1. Field of the Invention
The present invention relates to a muffler, and more particular to a muffler having an outer tube and an inner tube securely mounted inside the outer tube. The inner tube has multiple through holes defined in a periphery thereof and multiple shrink throats formed therein. Multiple baffles are provided between the outer tube and inner tube and each having multiple holes defined to communicate with spaces defined by the baffles. When the engine is in operation, the discontinuous discharge exhaust air from the engine will fill in the spaces and therefore generates a backpressure, which increases the resistance to the discharge of the exhaust. Before the piston of the engine is reaching the bottom dead center, said backpressure can reduce the power loss due to the early opening of the exhaust valve in the power (expansion) stroke. When the exhaust air passes the shrink throats, the speed of the exhaust air is increased (by the Venturi Tube Theory, P1V1=P2V2). After the exhaust air passes through the first shrink throat, because of the increase in the speed of the exhaust air, the air in the first space is sucked in, therefore builds up a pressure before the second shrink throat. As said process goes on, the exhaust function is discharged thoroughly.
2. Prior Art Description
Generally speaking, there are four different strokes in an engine when generating power: intake, compression, expansion and exhaust. When the piston of the engine is moving from the bottom dead center (BDC) to a top dead center (TDC), the engine is processing either the compression stroke or the exhaust stroke. When the piston is moving nearly to the TDC, the intake valve and exhaust valve are closed to start the expansion stroke. The sudden pressure generated by the explosion caused by the sparking plug will push the piston back to the BDC to be ready for the next stroke, the exhaust stroke. However, in order to discharge the exhaust function from the expansion stroke, the exhaust valve will be opening before the piston reaches the BDC. The early opening of the exhaust valve will cause a loss to a portion of the power generated from the expansion stroke. To avoid such situation, the exhaust valve should be opening as late as possible. However, another problem arises should the exhaust valve be opening too late. That is, if the exhaust valve be opening too late, the exhaust function from the expansion stroke will not be able to discharge thoroughly, which will hinder the exhaust stroke to process properly. Consequently, the entire exhaust stroke procedure will be influenced seriously. This dilemma troubles engine designers.
It is an objective of the invention to provide an improved muffler to obviate and mitigate the aforementioned problems.
The primary objective of the invention is to provide an improved muffler to provide a sufficient backpressure to reduce the power loss in the expansion stroke.
Another objective of the invention is to increase the speed of the exhaust air to reach the requirement of discharging the exhaust function thoroughly in the exhaust stroke.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.